Non-Aqueous Electrolyte Solution For Lithium Secondary Battery And Lithium Secondary Battery Including The Same

ABSTRACT

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same, and particularly, to a non-aqueous electrolyte solution for a lithium secondary battery which includes an ionizable lithium salt, an organic solvent, and an additive, wherein the additive includes tetravinylsilane, lithium difluorophosphate, and 1,3-propylene sulfate in a weight ratio of 1:3 to 20:3 to 20, and a total amount of the additive is in a range of 1 wt % to 4 wt % based on a total weight of the non-aqueous electrolyte solution for a lithium secondary battery, and a lithium secondary battery including the same.

TECHNICAL FIELD Cross-Reference to Related Applications

This application claims the benefit of Korean Patent Application Nos.2017-0010043, filed on Jan. 20, 2017, and 2018-0006125, filed on Jan.17, 2018, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated herein in its entirety by reference.

Technical Field

The present invention relates to a non-aqueous electrolyte solution fora lithium secondary battery and a lithium secondary battery includingthe same.

BACKGROUND ART

Recently, interests in energy storage technologies have beenincreasingly grown, and efforts for the development of high-capacityelectrochemical devices have been gradually materialized as theapplication of the energy storage technologies is expanded to mobilephones, camcorders, notebook PCs, and even to electric vehicles.

There emerges an interest in rechargeable secondary batteries amongthese electrochemical devices, and, particularly, lithium secondarybatteries developed in the early 1990's are spotlighted because thelithium secondary batteries are advantageous in that they have higheroperating voltage and significantly higher energy density.

A lithium secondary battery is composed of a carbon negative electrodecapable of intercalating and deintercalating lithium ions, a positiveelectrode formed of a lithium-containing composite oxide, and anon-aqueous electrolyte solution in which a lithium salt is dissolved ina mixed organic solvent.

In the lithium secondary battery, lithium ions react with theelectrolyte solution in a voltage range of 0.5 V to 3.5 V during initialcharge to form compounds, such as Li₂CO₃, Li₂O, and LiOH, and a solidelectrolyte interface (SEI), as a kind of a passivation layer, is formedon the surface of the negative electrode by these compounds.

The SEI film formed at an initial stage of charging may prevent areaction of the lithium ions with the carbon negative electrode or othermaterials during charge and discharge. Also, the SEI film may only passthe lithium ions by acting as an ion tunnel. Since the ion tunnel mayprevent the destruction of a structure of the carbon negative electrodedue to the co-intercalation of the carbon negative electrode and thenon-aqueous organic solvents having a high molecular weight whichsolvate lithium ions and moves therewith, cycle life characteristics andoutput characteristics of the lithium secondary battery may be improved.

In a case in which the organic solvent used in the non-aqueouselectrolyte solution of the lithium secondary battery is generallystored for a long period of time at high temperature, gas is generateddue to the occurrence of a side reaction of the organic solvent with atransition metal oxide of a discharged positive electrode activematerial. Furthermore, the negative electrode is exposed while the SEIfilm is gradually collapsed during high-temperature storage in a fullycharged state (e.g., storage at 60° C. after charged to 100% at 4.2 V),and the exposed negative electrode continuously reacts with theelectrolyte solution to generate gases, such as CO, CO₂, CH₄, and C₂H₆.

Battery swelling and deformation of an electrode assembly occur while aninternal pressure of the battery is increased by the gas thus generated,and, as a result, the battery may be deteriorated due to internal shortcircuit of the battery, or fire or explosion of the battery may occur.

In order to address these limitations, there is a need to develop anelectrolyte solution for a lithium secondary battery which may suppressthe side reaction during high-temperature storage.

Priot Art Documents

Japanese Patent Application Laid-open Publication No. 2010-116475

DISCLOSURE OF THE INVENTION Technical Problem

An aspect of the present invention provides a non-aqueous electrolytesolution for a lithium secondary battery which includes an additivecapable of forming a stable layer on the surface of an electrode andsuppressing an electrolyte solution side reaction duringhigh-temperature storage.

Another aspect of the present invention provides a lithium secondarybattery in which high-temperature storage characteristics and cycle lifecharacteristics are improved by including the non-aqueous electrolytesolution for a lithium secondary battery.

Technical Solution

According to an aspect of the present invention,

there is provided a non-aqueous electrolyte solution for a lithiumsecondary battery including an ionizable lithium salt; an organicsolvent; and an additive,

wherein the additive is a mixed additive which includes tetravinylsilane(TVS), lithium difluorophosphate (LiDFP), and 1,3-propylene sulfate(PPS) in a weight ratio of 1:3 to 20:3 to 20, and

the additive is included in an amount of 1 wt % to 4 wt % based on atotal weight of the non-aqueous electrolyte solution for a lithiumsecondary battery.

The weight ratio of the tetravinylsilane:the lithiumdifluorophosphate:the 1,3-propylene sulfate, as an additive, may be in arange of 1:3 to 17:5 to 20, for example, 1:5 to 15:5 to 20.

Also, the additive may be included in an amount of 1.8 wt % to 4 wt %based on the total weight of the non-aqueous electrolyte solution for alithium secondary battery.

Furthermore, the non-aqueous electrolyte solution of the presentinvention may further include at least one additional additive selectedfrom the group consisting of vinylene carbonate (VC), LiBF₄, 1,3-propanesultone, and tetraphenylborate.

The additional additive may be included in an amount of 0.1 wt % to 5 wt% based on the total weight of the non-aqueous electrolyte solution fora lithium secondary battery.

In a case in which the 1,3-propane sultone (PS) is included as theadditional additive, the tetravinylsilane and the 1,3-propane sultone(PS) may be included at a weight ratio of 1:5 to 1:15.

Also, in a case in which the VC or LiBF₄ is included as the additionaladditive, the tetravinylsilane and the VC or LiBF₄ may be included at aweight ratio of 1:1 to 1:3.

According to another aspect of the present invention,

there is provided a lithium secondary battery including a negativeelectrode, a positive electrode, a separator disposed between thenegative electrode and the positive electrode, and a non-aqueouselectrolyte solution,

wherein the non-aqueous electrolyte solution includes the non-aqueouselectrolyte solution for a lithium secondary battery of the presentinvention, and

the positive electrode includes a lithium-nickel-manganese-cobalt-basedoxide as a positive electrode active material.

Specifically, the positive electrode active material may include alithium transition metal oxide represented by Formula 1 below.

Li (Ni_(a)Co_(b)Mn_(c)) O₂   [Formula 1]

wherein, in Formula 1,

0.55≤a≤0.9, 0.05≤b≤0.22, 0.05≤c≤0.23, and a+b+c=1.

Typical examples of the positive electrode active material may be atleast one of Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂, Li(Ni_(0.7)Mn_(0.15)Co_(0.15)) O₂, and Li (Ni_(0.8)Mn_(0.1)Co_(0.1)) O₂.

Advantageous Effects

In the present invention, since a stable solid electrolyte interface(SEI) film may be formed on the surface of a negative electrode byincluding a mixed additive in which three types of compounds are mixedin a specific ratio, a non-aqueous electrolyte solution for a lithiumsecondary battery, in which a side reaction during high-temperaturestorage is suppressed, may be prepared. Also, a lithium secondarybattery may be prepared in which high-temperature storagecharacteristics and cycle life characteristics are improved by includingthe non-aqueous electrolyte solution.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail.

It will be understood that words or terms used in the specification andclaims should be interpreted as having a meaning that is consistent withtheir meaning in the context of the relevant art and the technical ideaof the invention, based on the principle that an inventor may properlydefine the meaning of the words or terms to best explain the invention.

Specifically, in an embodiment of the present invention, provided is anon-aqueous electrolyte solution for a lithium secondary batteryincluding:

an ionizable lithium salt; an organic solvent, and an additive,

wherein the additive is a mixed additive which includes tetravinylsilane(TVS), lithium difluorophosphate (LiDFP), and 1,3-propylene sulfate(PPS) in a weight ratio of 1:3 to 20:3 to 20, and

the additive is included in an amount of 1 wt % to 4 wt % based on atotal weight of the non-aqueous electrolyte solution for a lithiumsecondary battery.

First, in the non-aqueous electrolyte solution for a lithium secondarybattery according to the embodiment of the present invention, anylithium salt typically used in an electrolyte solution for a lithiumsecondary battery may be used as the ionizable lithium salt withoutlimitation, and, for example, the lithium salt may include Li⁺ as acation, and may include at least one selected from the group consistingof F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, N(CN)₂ ⁻, BF₄ ⁻, ClO₄ ⁻, AlO₄ ⁻, AlCl₄ ⁻,PF₆ ⁻, SbF₆ ⁻, AsF₆ ⁻, B₁₀Cl₁₀ ⁻, BF₂C₂O₄ ⁻, BC₄O₈ ⁻, PF₄C₂O₄ ⁻, PF₂C₄O₈⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻, CF₃SO₃ ⁻,C₄F₉SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, CF₃CF₂ (CF₃)₂CO⁻,(CF₃SO₂)₂CH⁻, CH₃SO₃ ⁻, CF₃ (CF₂)₇SO₃ ⁻, CF₃CO₂ ⁻, CH₃CO₂ ⁻, SCN⁻, and(CF₃CF₂SO₂)₂N⁻ as an anion. Specifically, the lithium salt may include asingle material selected from the group consisting of LiCl, LiBr, LiI,LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LPF₆, LiCF₃SO₃, LiCH₃CO₂, LiCF₃CO₂, LiAsF₆,LiSbF₆, LiAlCl₄, LiAlO₄, and LiCH₃SO₃, or a mixture of two or morethereof, and, in addition thereto, a lithium salt, such as a lithiumimide salt represented by lithium bisperfluoroethanesulfonimide (LiBETI,LiN(SO₂C₂F₅)₂), lithium fluorosulfonyl imide (LiFSI, LiN(SO₂F)₂), andlithium (bis)trifluoromethanesulfonimide (LiTFSI, LiN(SO₂CF₃)₂) whichare typically used in the electrolyte solution of the lithium secondarybattery, may be used without limitation. Specifically, the lithium saltmay include a single material selected from the group consisting ofLiPF₆, LiBF₄, LiCH₃CO₂, LiCF₃CO₂, LiCH₃SO₃, LiFSI, LiTFSI, and LiBETI,or a mixture of two or more thereof. However, the lithium salt does notinclude LiDFP which is included as the mixed additive.

The lithium salt may be appropriately changed in a normally usablerange, but may specifically be included in a concentration of 0.1 M to 3M, for example, 0.8 M to 2.5 M in the electrolyte solution. In a case inwhich the concentration of the lithium salt is greater than 3 M, afilm-forming effect may be reduced.

Also, in the non-aqueous electrolyte solution for a lithium secondarybattery according to the embodiment of the present invention, a type ofthe organic solvent is not limited as long as it may minimizedecomposition due to an oxidation reaction during charge and dischargeof the secondary battery and may exhibit desired characteristics withthe additive. For example, an ether-based solvent, an ester-basedsolvent, or an amide-based solvent may be used alone or in mixture oftwo or more thereof.

As the ether-based solvent among the organic solvents, any one selectedfrom the group consisting of dimethyl ether, diethyl ether, dipropylether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, ora mixture of two or more thereof may be used, but the present inventionis not limited thereto.

Furthermore, the ester-based solvent may include at least one compoundselected from the group consisting of a cyclic carbonate compound, alinear carbonate compound, a linear ester compound, and a cyclic estercompound.

Among these compounds, specific examples of the cyclic carbonatecompound may be any one selected from the group consisting of ethylenecarbonate (EC), 1,2-butylene carbonate, 2,3-butylene carbonate,1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate,and fluoroethylene carbonate (FEC), or a mixture of two or more thereof,and the cyclic carbonate compound may specifically include any oneselected from the group consisting of ethylene carbonate, 1,2-butylenecarbonate, 2,3-butylene carbonate, vinylene carbonate, andfluoroethylene carbonate (FEC), or a mixture of two or more thereof.

With respect to propylene carbonate (PC) among the cyclic carbonatecompounds, since the propylene carbonate causes an irreversibledecomposition reaction with a carbon-based negative electrode materialand an electrode exfoliation phenomenon caused by the propylenecarbonate occurs during high-temperature cycling depending on athickness of the electrode, capacity of the lithium secondary batterymay be reduced. Particularly, in a case in which the propylene carbonateis used with the lithium salt such as

LiPF₆, since the solvated propylene carbonate are not separated fromlithium ions in a process of forming the SEI film on the surface of thecarbon-based negative electrode and a process of intercalating thelithium ions solvated by the propylene carbonate between carbon layers,the solvated propylene carbonate and the lithium ions are intercalatedwhile breaking the negative electrode layers, and thus, an enormousamount of irreversible reaction may occur. In addition, since a robustSEI film is not formed on the surface of the negative electrode, workingof the lithium secondary battery may not be smooth.

Thus, the non-aqueous electrolyte solution for a lithium secondarybattery of the present invention may have an effect of improvinghigh-temperature storage characteristics and cycle characteristics byincluding ethylene carbonate having a high melting point, as anessential component, instead of including propylene carbonate as thecyclic carbonate compound.

Also, specific examples of the linear carbonate compound may be any oneselected from the group consisting of dimethyl carbonate (DMC), diethylcarbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC),methylpropyl carbonate, and ethylpropyl carbonate, or a mixture of twoor more thereof, and the linear carbonate compound may specificallyinclude any one selected from the group consisting of dimethylcarbonate, diethyl carbonate, dipropyl carbonate, and ethylmethylcarbonate, or a mixture of two or more thereof.

Specific examples of the linear ester compound may be any one selectedfrom the group consisting of methyl acetate, ethyl acetate, propylacetate, methyl propionate, ethyl propionate, propyl propionate, andbutyl propionate, or a mixture of two or more thereof, but the presentinvention is not limited thereto.

Specific examples of the cyclic ester compound may be any one selectedfrom the group consisting of γ-butyrolactone, γ-valerolactone,γ-caprolactone, σ-valerolactone, and ϵ-caprolactone, or a mixture of twoor more thereof, but the present invention is not limited thereto.

It is known that the cyclic carbonate-based compound among theester-based solvents is a solvent which well dissociates the lithiumsalt in the electrolyte due to high permittivity as a highly viscousorganic solvent. Also, an electrolyte solution having high electricalconductivity may be prepared when the cyclic carbonate-based compound ismixed with the low viscosity, low permittivity linear carbonate-basedcompound, such as dimethyl carbonate and diethyl carbonate, and thelinear ester-based compound in an appropriate ratio.

The cyclic carbonate-based compound and the linear carbonate-basedcompound may be mixed and used as the organic solvent, and a weightratio of the cyclic carbonate-based compound : the linearcarbonate-based compound in the organic solvent may be in a range of10:90 to 70:30.

Also, in the non-aqueous electrolyte solution for a lithium secondarybattery according to the embodiment of the present invention,tetravinylsilane (TVS) represented by the following Formula 2, as one ofthe additive components, is a compound that may form a robust SEI filmon the surface of the negative electrode through physical adsorption andelectrochemical reaction, wherein, since an increase in resistancecaused by an additional reaction of the electrolyte solution at hightemperature may be suppressed by the tetravinylsilane, thetetravinylsilane may improve durability of the lithium secondary batteryduring high-temperature storage.

Furthermore, lithium difluorophosphate represented by the followingFormula 3, as one of the additive components, is a component which iselectrochemically decomposed on the surfaces of positive electrode andnegative electrode to help the formation of the SEI. The lithiumdifluorophosphate may have an effect of improving long-term cycle lifecharacteristics of the secondary battery.

Also, as one of the additive components, 1,3-propylene sulfaterepresented by the following Formula 4 may form a stable protectivelayer on the surface of the negative electrode which does not crack evenduring high-temperature storage. The negative electrode coated with theprotective layer may prevent gas generation by suppressing thedecomposition of the non-aqueous organic solvent by a negative electrodeactive material even in a case in which a highly crystallized carbonmaterial, such as natural graphite or artificial graphite, is used asthe negative electrode active material or even during high-temperaturestorage. Furthermore, the protective layer does not interfere with acharge/discharge reaction of the battery. Thus, performance, such ascycle life, capacity, and resistance, as well as stabilities at roomtemperature and high temperature of the secondary battery may beimproved.

Furthermore, as the mixed additive, the tetravinylsilane, the lithiumdifluorophosphate, and the 1,3-propylene sulfate may specifically beincluded in a weight ratio of 1:3 to 17:5 to 20, for example, 1:5 to15:5 to 20.

In a case in which the weight ratio of the tetravinylsilane is greaterthan the above range, since the surplus tetravinylsilane causes a sidereaction to increase the resistance of the battery, cycle lifecharacteristics may be reduced. In contrast, the weight ratio of thetetravinylsilane is less than the above range, a gas generation reducingeffect and a SEI film forming effect are insignificant.

Also, in a case in which the weight ratio of the lithiumdifluorophosphate is greater than 20 or the weight ratio of the1,3-propylene sulfate is greater than 20 based on 1 part by weight ofthe tetravinylsilane, since internal resistance of the battery isincreased due to the excessive use of the additive, the cycle lifecharacteristics are reduced.

In a case in which the weight ratio of the lithium difluorophosphate and1,3-propylene sulfate is less than 3 based on 1 part by weight of thetetravinylsilane, since a stabilizing effect during the formation of theSEI film is insignificant, the high-temperature storage characteristicsand cycle life characteristics may be reduced.

From these results, in the non-aqueous electrolyte solution of thepresent invention, in a case in which the weight ratio of the compoundsconstituting the mixed additive satisfies the above range, a stable SEIfilm may be formed without an increase in the resistance, and,accordingly, an effect of suppressing an electrolyte solution sidereaction may be obtained.

Furthermore, a total amount of the additive of the present invention maybe in a range of 1 wt % to 4 wt %, for example, 1.8 wt % to 4 wt % basedon the total weight of the non-aqueous electrolyte solution for alithium secondary battery.

The amount of the additive in the non-aqueous electrolyte solution maybe determined by reaction specific surface areas of the positiveelectrode and the negative electrode, wherein, in a case in which theamount of the additive is 1 wt % or more as described above, expectedeffects resulting from the addition of each component may be met, forexample, a stable SEI film may not only be formed on the surface of thenegative electrode, but the gas generation reducing effect may also beachieved by suppressing the decomposition of the electrolyte solutioncaused by the reaction between the electrolyte solution and the negativeelectrode. Also, in a case in which the amount of the additive is 4 wt %or less, the gas generation reducing effect may not only be improved,but a stable SEI film may also be formed on the surface of the electrodewhile preventing a side reaction due to the excessive use of theadditive and the resulting increase in resistance.

In a case in which the amount of the additive is greater than 4 wt %,the gas generation reducing effect may be further improved due to theexcessive use of the additive, but, since an excessively thick layer isformed as the excessive amount of each component remains, an increase inresistance and a degradation in output may occur.

Thus, in a case in which the non-aqueous electrolyte solution accordingto the embodiment of the present invention includes the additive in anamount of 1 wt % to 4 wt % based on the total weight of the non-aqueouselectrolyte solution while including the tetravinylsilane, the lithiumdifluorophosphate, and the 1,3-propylene sulfate, as the additive, in aweight ratio of 1:3 to 20:3 to 20, the decomposition of the electrolytesolution due to the reaction between the electrolyte solution and thenegative electrode is minimized by forming a stable SEI film on thesurface of the negative electrode, and accordingly, characteristics ofthe secondary battery may be improved.

Also, the non-aqueous electrolyte solution according to the embodimentof the present invention may further include an additional additive, ifnecessary, in order to further obtain effects of improving cycle lifecharacteristics, low-temperature high-rate discharge characteristics,high-temperature stability, overcharge protection, and high-temperatureswelling.

The additional additive is not particularly limited as long as it is anadditive that may form a stable layer on the surfaces of the positiveelectrode and the negative electrode while not significantly increasinginitial resistance.

The additional additive may include at least one selected from the groupconsisting of vinylene carbonate (VC), LiBF₄, 1,3-propane sultone (PS),and tetraphenylborate (TPB).

In a case in which the 1,3-propane sultone (PS) is included among theadditional additives, a weight ratio of the tetravinylsilane : the1,3-propane sultone (PS) is in a range of 1:5 to 1:15.

In a case in which the VC or LiBF₄ is included as the additionaladditive, a weight ratio of the tetravinylsilane : the VC or LiBF₄ is ina range of 1:1 to 1:3.

Particularly, the additional additive may be included in an amount of0.1 wt % to 5 wt %, for example, 0.1 wt % to 4 wt % based on the totalweight of the non-aqueous electrolyte solution for a lithium secondarybattery. In a case in which the amount of the additional additive isless than 0.1 wt %, the effects to be achieved from the additionaladditive may be insignificant, and, in a case in which the amount of theadditional additive is greater than 5 wt %, a side reaction due to thesurplus additional additive may occur.

In general, in the secondary battery, lithium ions from a lithium metaloxide used as a positive electrode are intercalated while moving to acarbon-based electrode used as a negative electrode during initialcharge, wherein, since the lithium ions are highly reactive, the lithiumions react with the carbon-based negative electrode and an electrolytesolution to form an organic material, Li₂CO₃, LiO, or LiOH, and thesematerials form an SEI film on the surface of the negative electrode.Once the SEI film is formed during initial charge, the SEI film may actas an ion tunnel that only passes the lithium ions between theelectrolyte solution and the negative electrode while preventing areaction of the lithium ions with the carbon-based negative electrode orother materials during repeated charge and discharge caused by thesubsequent use of the battery. Since the SEI film blocks the movement ofan organic solvent for an electrolyte solution having a high molecularweight, for example, EC, DMC, DEC, or PP, to the carbon-based negativeelectrode by the ion tunnel effect, these organic solvents are notinserted into the carbon. based negative electrode together with lithiumions, so that. collapse of the structure of the carbon-based negativeelectrode can be prevented. That is, once the SEI film is formed, sincethe side reaction of the lithium ions with the carbon-based negativeelectrode or other materials does not occur again, an amount of thelithium ions, which is required during the charge and discharge causedby the subsequent use of the battery, may be reversibly maintained.

In other words, since a carbon material of the negative electrode reactswith the electrolyte solution during initial charge to form apassivation layer, it allows stable charge and discharge to bemaintained without further decomposition of the electrolyte solution,and, in this case, the quantity of electric charge consumed for theformation of the passivation layer on the surface of the negativeelectrode is irreversible capacity, wherein it has features that do notreact reversibly during discharge, and, for this reason, the lithium ionbattery no longer exhibits an irreversible reaction after the initialcharge reaction and may maintain a stable life cycle.

However, in a case in which the lithium secondary battery is stored athigh temperature in a fully charged state (e.g., storage at 60° C. aftercharged to 100% at 4.2 V or more), it is disadvantageous in that the SEIfilm is gradually collapsed by electrochemical energy and thermal energywhich are increased over time.

The collapse of the SEI film allows the surface of the negativeelectrode to be exposed, the exposed surface of the negative electrodeis decomposed as it reacts with the carbonate-based solvent in theelectrolyte solution, and thus, a continuous side reaction occurs.

The side reaction may continuously generate gas, and major gasesgenerated in this case may be CO, CO₂, CH₄, and C₂H₆, wherein the gasesgenerated may vary depending on the type of the negative electrodeactive material and, regardless of the type, the continuous gasgeneration increases the internal pressure of the lithium ion battery sothat it becomes a cause of swelling of a battery thickness.

Thus, in the present invention, since the tetravinylsilane, the lithiumdifluorophosphate, and the 1,3-propylene sulfate are mixed in theabove-described ratio and used as the additive during the preparation ofthe non-aqueous electrolyte solution, a stable layer is formed on thesurface of the electrode to suppress the electrolyte solution sidereaction, and thus, battery swelling during high-temperature storage maybe prevented and battery characteristics may be improved.

Also, in an embodiment of the present invention,

there is provided a lithium secondary battery including a negativeelectrode, a positive electrode, a separator disposed between thenegative electrode and the positive electrode, and a non-aqueouselectrolyte solution,

wherein the non-aqueous electrolyte solution includes the non-aqueouselectrolyte solution of the present invention, and

the positive electrode includes a lithium-nickel-manganese-cobalt-basedoxide as a positive electrode active material.

Specifically, in the lithium secondary battery of the present invention,an electrode assembly may be prepared by sequentially stacking thepositive electrode, the negative electrode, and the separator disposedbetween the positive electrode and the negative electrode, and, in thiscase, those prepared by a typical method and used in the preparation ofthe lithium secondary battery may all be used as the positive electrode,the negative electrode, and the separator which constitute the electrodeassembly.

First, the positive electrode may be prepared by forming a positiveelectrode material mixture layer on a positive electrode collector. Thepositive electrode material mixture layer may be formed by coating thepositive electrode collector with a positive electrode slurry includinga positive electrode active material, a binder, a conductive agent, anda solvent, and then drying and rolling the coated positive electrodecollector.

The positive electrode collector is not particularly limited so long asit has conductivity without causing adverse chemical changes in thebattery, and, for example, stainless steel, aluminum, nickel, titanium,fired carbon, or aluminum or stainless steel that is surface-treatedwith one of carbon, nickel, titanium, silver, or the like may be used.

Also, the positive electrode active material may include a lithiumtransition metal oxide represented by Formula 1 below.

Li (Ni_(a)Co_(b)Mn_(c)) O₂   [Formula 1]

wherein, in Formula 1,

0.55≤a≤0.9, 0.05≤b≤0.22, 0.05≤c≤0.23, and a+b+c=1.

Typical examples of the positive electrode active material may beLi(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂, Li (Ni_(0.7)Mn_(0.15)Co_(0.15)) O₂, orLi (Ni_(0.8)Mn_(0.2)Co_(0.1)) O₂.

Furthermore, in addition to the lithium transition metal oxiderepresented by Formula 1, the positive electrode active material mayfurther include any one of lithium-manganese-based oxide (e.g., LiMnO₂,LiMn₂O₄, etc.), lithium-cobalt-based oxide (e.g., LiCoO₂, etc.),lithium-nickel-based oxide (e.g., LiNiO₂, etc.),lithium-nickel-manganese-based oxide (e.g., LiNi_(1-Y)Mn_(Y)O₂ (where0<Y<1), LiMn_(2-Z)Ni_(z)O₄ (where 0<Z<2), etc.),lithium-nickel-cobalt-based oxide (e.g., LiNi_(1-Y1)Co_(Y1)O₂ (where1<Y1<1), lithium-manganese-cobalt-based oxide (e.g.,LiCo_(1-Y2)Mn_(Y2)O₂ (where 0<Y2<1), LiMn_(2-Z1)Co_(z1)O₄ (where1<Z1<2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide(e.g., Li (Ni_(p2)Co_(q2)Mn_(r3)M_(S2)) O₂ (where M is selected from thegroup consisting of aluminum (Al), iron (Fe), vanadium (V), chromium(Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo),and p2, q2, r3, and s2 are atomic fractions of each independentelements, wherein 0<p2<1, 0<q2<1, 0<r3<1, 0<S2<1, and p2+q2+r3+S2=1),etc.) or a compound of two or more thereof, if necessary.

The positive electrode active material may include LiCoO₂, LiMnO₂,LiNiO₂, or lithium nickel cobalt aluminum oxide (e.g.,Li(Ni_(0.8)Co_(0.15)Al_(0.05))O₂, etc.).

The positive electrode active material may be included in an amount of80 wt % to 99 wt %, for example, 93 wt % to 98 wt %, based on a totalweight of solid content in the positive electrode slurry. In a case inwhich the amount of the positive electrode active material is 80 wt % orless, since energy density is decreased, capacity may be reduced.

The binder is a component that assists in the binding between the activematerial and the conductive agent and in the binding with the currentcollector, wherein the binder is commonly added in an amount of 1 wt %to 30 wt % based on the total weight of the solid content in thepositive electrode slurry. Examples of the binder may be polyvinylidenefluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch,hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone,tetrafluoroethylene, polyethylene, polypropylene, anethylene-propylene-diene terpolymer (EPDM), a sulfonated EPDM, astyrene-butadiene rubber, a fluoro rubber, various copolymers, and thelike.

Any conductive agent may be used as the conductive agent withoutparticular limitation so long as it has conductivity without causingadverse chemical changes in the battery, and, for example, a conductivematerial, such as: carbon powder such as carbon black, acetylene black,Ketjen black, channel black, furnace black, lamp black, or thermalblack; graphite powder such as natural graphite with a well-developedcrystal structure, artificial graphite, or graphite; conductive fiberssuch as carbon fibers or metal fibers; metal powder such as fluorocarbonpowder, aluminum powder, and nickel powder; conductive whiskers such aszinc oxide whiskers and potassium titanate whiskers; conductive metaloxide such as titanium oxide; or polyphenylene derivatives, may be used.

The conductive agent is commonly added in an amount of 1 wt % to 30 wt %based on the total weight of the solid content in the positive electrodeslurry.

Those sold under the names, such as acetylene black-based products(Chevron Chemical Company, Denka black (Denka Singapore PrivateLimited), or Gulf Oil Company), Ketjen black, ethylene carbonate(EC)-based products (Armak Company), Vulcan XC-72 (Cabot Company), andSuper P (Timcal Graphite & Carbon), may be used as the conductive agent.

The solvent may include an organic solvent, such asN-methyl-2-pyrrolidone (NMP), and may be used in an amount such thatdesirable viscosity is obtained when the positive electrode activematerial as well as selectively the binder and the conductive agent areincluded. For example, the solvent may be included in an amount suchthat a concentration of the solid content in the slurry including thepositive electrode active material as well as selectively the binder andthe conductive agent is in a range of 10 wt % to 70 wt %, for example,20 wt % to 60 wt %.

Also, the negative electrode may be prepared by forming a negativeelectrode material mixture layer on a negative electrode collector. Thenegative electrode material mixture layer may be formed by coating thenegative electrode collector with a negative electrode slurry includinga negative electrode active material, a binder, a conductive agent, anda solvent, and then drying and rolling the coated negative electrodecollector.

The negative electrode collector generally has a thickness of 3 μm to500 μm. The negative electrode collector is not particularly limited solong as it has high conductivity without causing adverse chemicalchanges in the battery, and, for example, copper, stainless steel,aluminum, nickel, titanium, fired carbon, copper or stainless steel thatis surface-treated with one of carbon, nickel, titanium, silver, or thelike, an aluminum-cadmium alloy, or the like may be used. Also, similarto the positive electrode collector, the negative electrode collectormay have fine surface roughness to improve bonding strength with thenegative electrode active material, and the negative electrode collectormay be used in various shapes such as a film, a sheet, a foil, a net, aporous body, a foam body, a non-woven fabric body, and the like.

Furthermore, the negative electrode active material may include at leastone selected from the group consisting of lithium metal, a carbonmaterial capable of reversibly intercalating/deintercalating lithiumions, metal or an alloy of lithium and the metal, a metal compositeoxide, a material which may be doped and undoped with lithium, and atransition metal oxide.

As the carbon material capable of reversiblyintercalating/deintercalating lithium ions, a carbon-based negativeelectrode active material generally used in a lithium ion secondarybattery may be used without particular limitation, and, as a typicalexample, crystalline carbon, amorphous carbon, or both thereof may beused. Examples of the crystalline carbon may be graphite such asirregular, planar, flaky, spherical, or fibrous natural graphite orartificial graphite, and examples of the amorphous carbon may be softcarbon (low-temperature sintered carbon) or hard carbon, mesophase pitchcarbide, and fired cokes.

As the metal or the alloy of lithium and the metal, a metal selectedfrom the group consisting of copper (Cu), nickel (Ni), sodium (Na),potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium(Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si),antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium(Ra), germanium (Ge), aluminum (Al), and tin (Sn), or an alloy oflithium and the metal may be used.

One selected from the group consisting of PbO, PbO₂, Pb₂O₃, Pb₃O₄,Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, Bi₂O₅, Li_(x)Fe₂O₃ (0≤v≤1), Li_(x)WO₂ (0≤x≤1) , and Sn_(x)Me_(1-x)Me′_(y)O_(z) (Me:manganese (Mn),Fe, Pb, or Ge; Me′: Al, boron (B), phosphorus (P), Si, Groups I, II andIII elements of the periodic table, or halogen; 0<x≤1; 1≤y≤3; 1≤z≤8) maybe used as the metal composite oxide.

The material, which may be doped and undoped with lithium, may includeSi, SiO_(x) (0<x<2), a Si—Y alloy (where Y is an element selected fromthe group consisting of alkali metal, alkaline earth metal, a Group 13element, a Group 14 element, transition metal, a rare earth element, anda combination thereof, and is not Si), Sn, SnO₂, and Sn—Y (where Y is anelement selected from the group consisting of alkali metal, alkalineearth metal, a Group 13 element, a Group 14 element, transition metal, arare earth element, and a combination thereof, and is not Sn), and amixture of SiO₂ and at least one thereof may also be used. The element Ymay be selected from the group consisting of Mg, Ca, Sr, Ba, Ra,scandium (Sc), yttrium (Y), Ti, zirconium (Zr), hafnium (Hf),rutherfordium (Rf), V, niobium (Nb), Ta, dubidium (Db), Cr, Mo, tungsten(W), seaborgium (Sg), technetium (Tc), rhenium (Re), bohrium (Bh), Fe,Pb, ruthenium (Ru), osmium (Os), hassium (Hs), rhodium (Rh), iridium(Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn,cadmium (Cd), B, Al, gallium (Ga), Sn, In, Ge, P, arsenic (As), Sb,bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po),and a combination thereof.

The transition metal oxide may include lithium-containing titaniumcomposite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

The negative electrode active material may be included in an amount of80 wt % to 99 wt % based on a total weight of solid content in thenegative electrode slurry.

The binder is a component that assists in the binding between theconductive agent, the active material, and the current collector,wherein the binder is commonly added in an amount of 1 wt % to 30 wt %based on the total weight of the solid content in the negative electrodeslurry. Examples of the binder may be polyvinylidene fluoride, polyvinylalcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, an ethylene-propylene-diene polymer (EPDM),a sulfonated EPDM, a styrene-butadiene rubber, a fluoro rubber, andvarious copolymers thereof.

The conductive agent is a component for further improving theconductivity of the negative electrode active material, wherein theconductive agent may be added in an amount of 1 wt % to 20 wt % based onthe total weight of the solid content in the negative electrode slurry.Any conductive agent may be used without particular limitation so longas it has conductivity without causing adverse chemical changes in thebattery, and, for example, a conductive material, such as: carbon powdersuch as carbon black, acetylene black, Ketjen black, channel black,furnace black, lamp black, or thermal black; graphite powder such asnatural graphite with a well-developed crystal structure, artificialgraphite, or graphite; conductive fibers such as carbon fibers or metalfibers; metal powder such as fluorocarbon powder, aluminum powder, andnickel powder; conductive whiskers such as zinc oxide whiskers andpotassium titanate whiskers; conductive metal oxide such as titaniumoxide; or polyphenylene derivatives, may be used.

The solvent may include water or an organic solvent, such as NMP andalcohol, and may be used in an amount such that desirable viscosity isobtained when the negative electrode active material as well asselectively the binder and the conductive agent are included. Forexample, the solvent may be included in an amount such that aconcentration of the solid content in the negative electrode slurryincluding the negative electrode active material as well as selectivelythe binder and the conductive agent is in a range of 50 wt % to 75 wt %,for example, 50 wt % to 65 wt %.

Also, a typical porous polymer film used as a typical separator, forexample, a porous polymer film prepared from a polyolefin-based polymer,such as an ethylene homopolymer, a propylene homopolymer, anethylene/butene copolymer, an ethylene/hexene copolymer, and anethylene/methacrylate copolymer, may be used alone or in a laminationtherewith as the separator, and a typical porous nonwoven fabric, forexample, a nonwoven fabric formed of high melting point glass fibers orpolyethylene terephthalate fibers may be used, but the present inventionis not limited thereto.

A shape of the lithium secondary battery of the present invention is notparticularly limited, but a cylindrical type using a can, a prismatictype, a pouch type, or a coin type may be used.

Hereinafter, the present invention will be described in more detailaccording to examples. However, the invention may be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these example embodiments areprovided so that this description will be thorough and complete, andwill fully convey the scope of the present invention to those skilled inthe art.

EXAMPLES Example 1 (Non-Aqueous Electrolyte Solution Preparation)

A non-aqueous electrolyte solution of the present invention was preparedby adding a mixed additive (0.2 g of tetravinylsilane, 1.0 g of lithiumdifluorophosphate, and 1.0 g of 1,3-propylene sulfate) to 97.8 g of anorganic solvent (ethylene carbonate (EC):ethyl methyl carbonate(EMC)=volume ratio of 3:7) in which 1 M LiPF₆ was dissolved (see Table 1below).

(Secondary Battery Preparation)

A positive electrode active material (Li(Ni_(0.6)Mn_(0.2)Co_(0.2)) O₂),a conductive agent (carbon black), and a binder (polyvinylidenefluoride) were added to N-methyl-2-pyrrolidone (NMP), as a solvent, at aweight ratio of 90:5:5 to prepare a positive electrode slurry (solidcontent of 40 wt %). One surface of a 20 μm thick positive electrodecollector (Al thin film) was coated with the positive electrode slurry,dried, and roll-pressed to prepare a positive electrode.

Subsequently, a negative electrode active material (artificialgraphite), a conductive agent (carbon black), and a binder(polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP), asa solvent, at a weight ratio of 90:5:5 to prepare a negative electrodeslurry (solid content of 40%). One surface of a 20 μm thick negativeelectrode collector (Cu thin film) was coated with the negativeelectrode slurry, dried, and roll-pressed to prepare a negativeelectrode.

Next, a coin-type battery was prepared by a typical method in which theabove-prepared positive electrode and negative electrode weresequentially stacked with a polyethylene porous film, and a lithiumsecondary battery (battery capacity 340 mAh) was then prepared byinjecting the prepared non-aqueous electrolyte solution of Example 1thereinto.

Example 2

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.1 g oftetravinylsilane, 1.5 g of lithium difluorophosphate, and 2 g of1,3-propylene sulfate were included as a mixed additive in 96.4 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Example 3 (Non-Aqueous Electrolyte Solution Preparation)

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.05 g oftetravinylsilane, 0.75 g of lithium difluorophosphate, and 1.0 g of1,3-propylene sulfate were included as an additive in 98.2 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Example 4

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.1 g oftetravinylsilane, 1.0 g of lithium difluorophosphate, and 1.5 g of1,3-propylene sulfate were included as an additive in 97.4 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Example 5

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.1 g oftetravinylsilane, 1.0 g of lithium difluorophosphate, and 1.0 g of1,3-propylene sulfate were included as an additive in 97.9 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Example 6

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.1 g oftetravinylsilane, 2.0 g of lithium difluorophosphate, and 1 g of1,3-propylene sulfate were included as a mixed additive in 96.9 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 1

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 3 g of vinylenecarbonate (VC) was included in 97 g of an organic solvent (ethylenecarbonate (EC):ethyl methyl carbonate (EMC)=volume ratio of 3:7), inwhich 1 M LiPF₆ was dissolved, during the preparation of the non-aqueouselectrolyte solution (see Table 1 below).

Comparative Example 2

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 2 g of LiBF₄ wasincluded in 98 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 3:7), in which 1 M LiPF₆ wasdissolved, during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 3

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Example 1 except that 0.5 g oftetravinylsilane, 1.25 g of lithium difluorophosphate, and 1.25 g of1,3-propylene sulfate were included as a mixed additive in 97 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 4

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 0.1g of tetravinylsilane, 0.5 g of lithium difluorophosphate, and 2.5 g of1,3-propylene sulfate were included as a mixed additive in 96.9 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 5

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 0.1g of tetravinylsilane, 0.3 g of lithium difluorophosphate, and 2.4 g of1,3-propylene sulfate were included as a mixed additive in 97.15 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 6

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 0.15g of tetravinylsilane, 2.1 g of lithium difluorophosphate, and 0.3 g of1,3-propylene sulfate were included as a mixed additive in 97.45 g of anorganic solvent during the preparation of the non-aqueous electrolytesolution (see Table 1 below).

Comparative Example 7

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 1.5g of lithium difluorophosphate and 1.5 g of 1,3-propylene sulfate wereincluded as a mixed additive in 97 g of an organic solvent during thepreparation of the non-aqueous electrolyte solution (see Table 1 below).

Comparative Example 8

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 0.25g of tetravinylsilane and 2.5 g of 1,3-propylene sulfate were includedas a mixed additive in 97.25 g of an organic solvent during thepreparation of the non-aqueous electrolyte solution (see Table 1 below).

Comparative Example 9

A non-aqueous electrolyte solution and a lithium secondary battery wereprepared in the same manner as in Comparative Example 3 except that 0.25g of tetravinylsilane and 2.5 g of lithium difluorophosphate wereincluded as a mixed additive in 97.25 g of an organic solvent during thepreparation of the non-aqueous electrolyte solution (see

Table 1 below).

Comparative Example 10

A negative electrode, a positive electrode, and a lithium secondarybattery including the negative electrode and the positive electrode wereprepared in the same manner as in Example 1 except that a lithium cobaltcomposite oxide (LiCoO₂) instead of Li (Ni_(0.6)Mn_(0.2)Co_(0.2)) O₂,was included as a positive electrode active material during thepreparation of the secondary battery.

EXPERIMENTAL EXAMPLES Experimental Example 1 Cycle Life CharacteristicTest

Each of the secondary batteries prepared in Examples 1 to 6 andComparative Examples 1 to 10 was charged at 1 C to 4.25 V/55 mA under aconstant current/constant voltage (CC/CV) condition at 45° C. and thendischarged at a constant current (CC) of 2 C to a voltage of 3.0 V(1,000 cycles/1 cycle×100) to measure 100 cycle lifetime at hightemperature, and the results thereof are presented in Table 1 below.

Also, each of the secondary batteries prepared in Examples 1 to 6 andComparative Examples 1 to 10 was charged at 1 C to 4.25 V/55 mA under aCC/CV condition at 25° C. and then discharged at a CC of 2 C to avoltage of 3.0 V (1,000 cycles/1 cycle×100) to measure 100 cycle lifecharacteristics at room temperature, and the results thereof arepresented in Table 1 below.

Experimental Example 2 High-Temperature Storage Characteristic Test

After each of the secondary batteries prepared in Examples 1 to 6 andComparative Examples 1 to 10 was stored at a high temperature of 60° C.for 16 weeks, each secondary battery was charged at 1 C. to 4.25 V/55 mAunder a constant current/constant voltage (CC/CV) condition at roomtemperature and then discharged at a constant current (CC) of C to avoltage of 2.5 V, and capacity after high-temperature storage wasmeasured by calculating discharge capacity after 16 weeks as apercentage (capacity after 16 weeks/initial discharge capacity×100 (%)).The results thereof are presented in Table 1 below.

Also, after each of the secondary batteries prepared in Examples 1 to 6and Comparative Examples 1 to 10 was stored at a high temperature of 60°C. for 16 weeks, output was measured by a voltage difference generatedby discharging each secondary battery at 3 C. for 10 seconds at a stateof charge (SOC) of 50% at room temperature, output after 16 weeksstorage was calculated as a percentage (output after 16 weeks/initialoutput×100), and the results thereof are presented in Table 1 below.

Furthermore, after each of the secondary batteries prepared in Examples1 to 6 and Comparative Examples 1 to 10 was stored at a high temperatureof 60° C. for 16 weeks, a change in thickness was measured, and theresults thereof are presented in Table 1 below.

TABLE 1 For-average electrolyte solution Organic solvent Amount Totalamount Positive electrode Type added Amount of additive added (g) ofactive material (volume ratio) (g) TVS LiDFP PPS Others additive (g)Example 1 Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 97.8 0.2 1.0 1.0 —2.2 Example 2 Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 96.4 0.1 1.52.0 — 3.6 Example 3 Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 98.20.05 0.75 1.0 — 1.8 Example 4 Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC =3:7 97.4 0.1 1.0 1.5 — 2.6 Example 5 Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂EC:EMC = 3:7 97.9 0.1 1.0 1.0 — 2.1 Example 6Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 96.9 0.1 2.0 1.0 — 3.1Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 97 — — — VC 3.0Example 1 3.0 Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 98— — — LiBF₄ 2.0 Example 2 2.0 Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂EC:EMC = 3:7 97 0.5 1.25 1.25 — 3.0 Example 3 ComparativeLi(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 96.9 0.1 0.5 2.5 — 3.1Example 4 Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 97.150.1 0.3 2.4 — 2.85 Example 5 Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂EC:EMC = 3:7 97.45 0.15 2.1 0.3 — 2.55 Example 6 ComparativeLi(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 97 — 1.5 1.5 — 3 Example 7Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:7 97.25 0.25 — 2.5— 2.75 Example 8 Comparative Li(Ni_(0.6)Mn_(0.2)Co_(0.2))O₂ EC:EMC = 3:797.25 0.25 0.25 — — 2.75 Example 9 Comparative LiCoO₂ EC:EMC = 3:7 97.80.2 1 1 — 2.2 Example 10 High-temperature storage characteristics (%)100 cycle life 16 weeks characteristics Battery (%) thickness Low- High-increase temperature temperature Capacity Output rate lifetime lifetimeExample 1 86.7 87.1 14 82.9 79.4 Example 2 87.2 91.1 13.7 81.4 78.8Example 3 89.5 92.9 15.8 81.1 76.7 Example 4 87.4 92.0 14.3 84.0 78.6Example 5 87.2 92.3 14.2 83.2 77.2 Example 6 80.7 81.7 17.3 78.5 72.4Comparative 65.8 67.2 vent 68.2 51.3 Example 1 Comparative 71.1 63.429.3 61.5 52.5 Example 2 Comparative 81.2 79.6 14.6 68.2 71.1 Example 3Comparative 80.7 81.5 18.3 66.3 64.2 Example 4 Comparative 81.3 78.118.4 64.8 63.1 Example 5 Comparative 81.3 80.6 19.7 74.8 69.3 Example 6Comparative 73.1 81.5 28.7 75.6 71.2 Example 7 Comparative 74.2 76.219.5 59.2 56.8 Example 8 Comparative 78.3 79.2 22.6 66.3 63.2 Example 9Comparative 72.8 77.2 31.7 67.6 66.2 Example 10

As illustrated in Table 1, when the life characteristics after 1,000cycles were examined, it may be confirmed that the secondary batteriesprepared in Examples 1 to 6 had significantly better room-temperatureand high-temperature cycle life characteristics than the secondarybatteries prepared in Comparative Examples 1 to 10.

Also, when the high-temperature storage characteristics were examined,it may be confirmed that capacity and output characteristics of thesecondary batteries prepared in Examples 1 to 6 were improved incomparison to those of the secondary batteries prepared in ComparativeExamples 1 to 10.

Particularly, with respect to the secondary battery of ComparativeExample 10 which included LCO as a positive electrode active material,since stability of the SEI film formed on the surface of the positiveelectrode was relatively lower than those of the secondary batteries ofExamples 1 to 6 including the lithium-nickel-manganese-cobalt-basedoxide, it may be understood that the cycle life characteristics andhigh-temperature storage characteristics were degraded.

1. A non-aqueous electrolyte solution for a lithium secondary battery,the non-aqueous electrolyte solution comprising: an ionizable lithiumsalt; an organic solvent; and an additive, wherein the additive is amixed additive which includes tetravinylsilane, lithiumdifluorophosphate, and 1,3-propylene sulfate in a weight ratio of 1:3 to20:3 to 20, and the additive is included in an amount of 1 wt % to 4 wt% based on a total weight of the non-aqueous electrolyte solution. 2.The non-aqueous electrolyte solution for a lithium secondary battery ofclaim 1, wherein the weight ratio of the tetravinylsilane:the lithiumdifluorophosphate:the 1,3-propylene sulfate is in a range of 1:3 to 17:5to
 20. 3. The non-aqueous electrolyte solution for a lithium secondarybattery of claim 1, wherein the weight ratio of the tetravinylsilane:thelithium difluorophosphate:the 1,3-propylene sulfate is in a range of 1:5to 15:5 to
 20. 4. The non-aqueous electrolyte solution for a lithiumsecondary battery of claim 1, wherein the additive is included in anamount of 1.8 wt % to 4 wt % based on the total weight of thenon-aqueous electrolyte solution for a lithium secondary battery.
 5. Thenon-aqueous electrolyte solution for a lithium secondary battery ofclaim 1, further comprising at least one additional additive selectedfrom the group consisting of vinylene carbonate, LiBF₄, 1,3-propanesultone, and tetraphenylborate.
 6. The non-aqueous electrolyte solutionfor a lithium secondary battery of claim 5, wherein the additionaladditive is included in an amount of 0.1 wt % to 5 wt % based on thetotal weight of the non-aqueous electrolyte solution.
 7. The non-aqueouselectrolyte solution for a lithium secondary battery of claim 5,wherein, in a case in which the 1,3-propane sultone is included as theadditional additive, a weight ratio of the tetravinylsilane:the1,3-propane sultone is in a range of 1:5 to 1:15.
 8. The non-aqueouselectrolyte solution for a lithium secondary battery of claim 5,wherein, in a case in which the vinylene carbonate or LiBF₄ is includedas the additional additive, a weight ratio of the tetravinylsilane:thevinylene carbonate or LiBF₄ is in a range of 1:1 to 1:3.
 9. A lithiumsecondary battery comprising a negative electrode, a positive electrode,a separator disposed between the negative electrode and the positiveelectrode, and a non-aqueous electrolyte solution, wherein thenon-aqueous electrolyte solution comprises the non-aqueous electrolytesolution for a lithium secondary battery of claim 1, and the positiveelectrode comprises a lithium-nickel-manganese-cobalt-based oxide as apositive electrode active material.
 10. The lithium secondary battery ofclaim 9, wherein the positive electrode active material comprises alithium transition metal oxide represented by Formula 1:Li (Ni_(a)Co_(b)Mn_(c)) O₂   [Formula 1] wherein, in Formula 1,0.55≤a≤0.9, 0.05≤b≤0.22, 0.05≤c≤0.23, and a+b+c=1.
 11. The lithiumsecondary battery of claim 10, wherein the positive electrode activematerial comprises at least one of Li (Ni_(0.6)Mn_(0.2)Co_(0.2))O₂, Li(Ni_(0.7)Mn_(0.15)Co_(0.15)) O₂, Li (Ni_(0.8)Mn_(0.1)Co_(0.1)) O₂.